Computer-generated imagery (CGI) has become such a staple of modern movie-making that most people know what actors are doing when prancing around in front of green screens wearing skin-tight leotards with reflective balls affixed at various locations over their bodies – motion capture.
In addition to the actor’s performance, such techniques can also require the tracking of camera movements and props so that perspective is maintained when translating the movements into CGI. Now researchers have demonstrated a system that can perform motion capture almost anywhere and without the need to track a separate camera and it does this by mounting the cameras on the actors instead.
The wearable camera system developed by researchers at Disney Research, Pittsburgh (DRP) and Carnegie Mellon University (CMU) reconstructs the relative and global motions of an actor using a process called ‘structure from motion’ (SfM). CMU professor of computer science and robotics Takeo Kanade developed SfM 20 years ago as a means of determining the three-dimensional structure of an object by analyzing the images from a camera as it moves around the object, or as the object moves past the camera.
For use in motion capture, SfM isn’t used primarily to analyze objects in the person’s surroundings, but to estimate the pose of the cameras on the person. The researchers used Velcro to mount 20 lightweight, outward-facing cameras on the limbs and trunk of each subject and calibrated each camera using a reference structure. When each person performed a range-of-motion exercise the system was able to automatically build a digital skeleton and estimate where the cameras were positioned in respect to that skeleton.
